DIY Digital Audio Player (DAP) Project No.2473 --- Part 2 ---

This is part two of my previous blog post featured here. In this part I conduct a distortion measurement comparison between the following: 

Test A 

  • Raspberry Pi 4 with Ian Canada 20B. TransportPi Digi Top Hat with SC-Pure Clock

Test B 

  • Raspberry Pi 4 USB Ouput to SMSL D300 DAC


I wanted to see if I could correlate my listening impressions with actual test data. Does the Ian Canada TransportPi Digi #20B with the SC-Pure clock upgrade provide improved distortion performance compared to simply using the USB out on the Raspberry Pi4? That’s what I wanted to find out. But to conduct the test required that I save my test signals to the attached USB thumb drive inserted into the Pi since this is how I normally listen to my music.

Choosing Test Signals 

Luckily my ARTA measurement software has a feature to export various test signals to .wav files. I decided to keep things simple and devised two test signals. 

  1. Dual sine tone of 60Hz + 7kHz using a 4:1 power ratio. 
  2. 12 band/octave multitone 20Hz-20kHz

Once the files were loaded up to my USB thumb drive they could be played back using the Volumio music player operating system installed on the Pi. 

Physical Test Setup 

The physical test setup is as follows: 

Rasberry Pi4 running Volumio OS, playing local test signal files via an attached USB thumb drive > SMSL D300 DAC > XLR Analogue out to E1DA Cosmos ADC > Windows Laptop running ARTA measurement software 

ARTA’s real time spectrum analyzer was set to “External” for the test signal source selection because the test signal was generated by the music server itself. 

TransportPi + SC-Pure Results 

I set the “Playback Options” within Volumio to HifiBerry+Digi Pro” which sends audio from the Pi via IS2 to the TransportPi Top Hat which then sends signal via Digital coax to the SMSL D300 DAC. 

Let's start with a dual sine tone of 60Hz + 7kHz using a 4:1 power ratio. We can see that the we have 120dB of dynamic range.


Bypassing the TransportPi required changing the output source in the Volumio software from “HifiBerry+DigiPro” to “SMSL USB Audio”. This requires turning off the IS2 output.

60Hz plus 7kHz Raspberry Pii 4 USB Ouput to SMSL D300 DAC Results

As you can see below there is virtually no change in the distortion performance when simply using the USB output from the Pi compared to using the Ian Canada TransportPi + SC-Pure Top Hat.


Testing with multiband multitone is shown below for the 20B TransportPi Digi with SC-Pure Clock is shown below. We see 92dB dynamic range.

Switching to the USB output of the Raspberry Pi 4 is shown below. There is no change in test performance when comparing the multiband test tone. 


As you can see there is no measurable distortion difference when upgrading to the Ian Canada top hat product (#20 TransportPi Digi with SC-Pure clock) compared to the direct USB connection between the Raspberry Pi and SMSL D300 DAC. I was hoping that there would be a measurable difference in performance so that I could continue to look at further music streamer upgrades. But this does not seem to be the case. If there are measurable differences to the upgrade then they are not revealed in this particular type of test or signal. It is my opinion that the upgrade offers a subjective improvement in sound quality, however confirming this through measurement simply eludes me. Was the test of any value? It is important to determine what doesn’t work so that one can consider what will work. Some may be cynical and simply tell me to listen with my ears. But I’ll point out that nobody is measuring streamer performance especially when it comes to playback performance from local storage. If I can establish a test metric that reveals sonic differences, then it might be a path towards even greater sonic purity. 


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